EP0600774B1 - Polyisocyanate mixture for the preparation of flexible highly elastic polyurethane foams - Google Patents

Abstract

The present invention relates to a mixture of polyisocyanates which comprises chemically modified tolylene diisocyanate and 1,6-hexamethylene diisocyanate. It also relates to the use of this mixture of polyisocyanates for the preparation of flexible highly elastic polyurethane foams.

Description

The present invention relates to a mixture of polyisocyanates making it possible to obtain flexible polyurethane foams of high elasticity.

It also relates to the use of this mixture of polyisocyanates for the preparation of flexible polyurethane foams of high elasticity.

Flexible polyurethane foams are known materials which are widely used. These foams are generally prepared from polyisocyanates and polyether polyols. They can be distinguished, according to their elastic properties, in so-called "standard" foams and in high elasticity foams. These foams can also include additives, such as in particular catalysts, surfactants and blowing agents.

Toluylene diisocyanate (TDI) is the polyisocyanate used for the preparation of so-called "standard" or traditional foams. TDI-80, consisting of an isomeric mixture of 80% by mass of the 2,4-isomer and 20% by mass of the 2,6-isomer, is the most commonly used mixture for this preparation. In certain cases, mixtures richer in 2,6 isomers of toluylene diisocyanate are also used, such as in particular the mixture corresponding to the 65/35 mass ratio of 2,4 and 2,6 isomers of toluylene diisocyanate. However, in certain applications of these foams, such as in particular padding, cushioning and cushioning, they are often accused of a lack of comfort. That is to say, a small variation in the compressive force applied to these foams is accompanied by a large variation in the deformation. This phenomenon can in particular be explained by the presence of a "plateau" on the deformation curve of the foams as a function of the compression exerted.

It is now possible to manufacture foams, called flexible foams of high elasticity, giving improved comfort. These are characterized by a deformation curve as a function of the compression applied, the shape of which is greatly reduced. They also exhibit less regular cellularization.

Different methods for preparing such foams can be used.

Thus, it is known, on the one hand, to modify the polyether polyol, usually used for the preparation of traditional foams. These modifications may consist in grafting onto the polyether polyol at least one unsaturated monomer, chosen in particular from styrene and acrylonitrile. Polyether polyols can also be brought into contact with organic fillers such as polyureas.

It is known, on the other hand, to modify toluylene diisocyanate (modified TDI) either by mixing it with crude diphenyl methane diisocyanate, or by replacing it with chemically modified toluylene diisocyanate.

However, by using these types of modified TDI, foams can be obtained which may have a residual deformation at too high a humidity, more particularly in the case of cold molding. The residual deformation is measured after compression at 70% deflection at 50 ° C and 95% relative humidity, according to standard NF-T56-112.

Furthermore, since the use of chlorofluorocarbons as agents for physical expansion has been banned from the international community, it has been known to replace them with chemical blowing agents such as water. However, the fact of increasing the amount of water in the process has the consequence of making the resulting foams more sensitive to wet residual deformation.

We can also blame these products foamed with water only, lacking flexibility or having an excess of lift. In fact, water promotes the formation, in the matrix of the polymer, of rigid segments of the urea type.

Finally, the foams obtained from a mixture of toluylene diisocyanate and crude diphenyl methane diisocyanate also exhibit poor resistance to tearing.

It is also known to replace toluylene diisocyanate or derivatives of diphenyl methane diisocyanate. However, the disadvantage of such a method is that it is necessary to use physical blowing agents to obtain low density foams.

The use of mixtures comprising toluyene diisocyanate in allophanate form, combined with isocyanates free of such bonds, to give flame retardant foams, is exemplified in US Patent 3,832,311. However, there is nothing to conclude that the use of such mixtures is suitable for obtaining flexible foams of high elasticity.

The object of the present invention is therefore to propose a new mixture of polyisccyanates which do not have the drawbacks mentioned above, and to obtain flexible polyurethane foams of high elasticity whose remanent deformation is significantly improved.

It has now been found that this object and others are achieved by the present invention which relates to a mixture of polyisocyanates comprising chemically modified toluylene diisocyanate and 1,6-hexamethylene diisocyanate the amount of which is between 0.5 and 30% by weight. weight of said mixture of isocyanates.

The invention also relates to the use of this mixture for the preparation of flexible polyurethane foams of high elasticity by implementing the process of polyaddition of isocyanates.

It has actually been observed that the use of the mixture according to the invention makes it possible to prepare flexible polyurethane foams of high elasticity having the advantages mentioned above.

These foams are therefore particularly well suited for the production of seats used in the automotive and furniture sectors.

In addition, the use of the mixture according to the invention advantageously makes it possible to conserve the foaming kinetics and not to increase the maximum pressure developed during the preparation of the foams. This last advantage is interesting for obtaining molded products, because it makes it possible to work with lighter molds and to limit the losses of raw materials at the jointing surfaces of the mold.

Furthermore, the foams obtained by using the mixture according to the invention advantageously have low densities, without the need to use physical blowing agents.

The first object of the invention therefore relates to a mixture of polyisocyanates comprising chemically modified toluylene diisocyanate and 1,6-hexamethylene diisocyanate.

The term chemically modified toluylene diisocyanate (or modified toluylene diisocyanate) means derivatives of toluylene diisocyanate comprising bonds of the allophanate, biuret, urethane, urea, carbodiimide or isocyanurate type.

These chemical modifications are implemented by any means known to those skilled in the art. Thus, to create isocyanurate type bonds, it is known to heat treat the isocyanate, in the presence, if necessary, of a catalyst. Among these, mention may in particular be made of phosphines, amines such as pyridine, or also Mannich bases. Furthermore, obtaining carbodiimide type bonds can be carried out by treating the isocyanate with a catalyst such as phospholine oxide. It is also possible to envisage reacting the isocyanate with at least one amine or water, to obtain urea-type bonds; these bonds can themselves be transformed by heat treatment, into biuret type bonds. Another possible modification of the isocyanate is to react it with a low molecular weight glycol or polyol to give urethane linkages; the latter can lead, by heating, to allophanate type bonds. Of course, all these examples are given for information only and do not in any way constitute an exhaustive list of the known means that can be used.

Any toluylene diisocyanate commonly used in foaming formulations can be chemically modified for further use in the blend of the present invention. The starting toluylene diisocyanate preferably corresponds to a mixture of the 2,4 and 2,6 isomers of toluylene diisocyanate. More particularly, the isomeric mixture of 80% by mass of the 2.4 isomer and 20% by mass of the 2.6 isomer is used.

The modified toluylene diisocyanate used in the present invention is preferably a biuretized toluylene diisocyanate, that is to say comprising biuret type bonds. It can be obtained by any means known per se, in particular by reacting toluylene diisocyanate with water or any compound, such as hydrated salts, releasing water at a temperature lower than that of destruction of the biuretized isocyanate. It can also be prepared, for example, by reaction with an easily dehydratable alcohol and preferably a tertiary alcohol, with an amine or with an easily lactonizable acid-alcohol.

These reactions can be carried out with or without solvent. As solvent suitable for obtaining biuretized toluylene diisocyanate, mention may be made, for example, of the compounds chosen from ketones such as acetone, methyl ethyl ketone.

The biuretized toluylene diisocyanate thus obtained, if appropriate after removal of the solvent, is usually in liquid form.

According to another characteristic of the invention, the chemically modified toluylene diisocyanate is only partially modified. Indeed, if, in the particular case of the preparation of flexible polyurethane foams, the toluylene diisocyanate used has a too low modification rate, the resistance of the gel to foaming will be insufficient. Furthermore, the elasticity of the foam obtained may be considered too low for the application. Conversely, if the rate of modification is too high, the foam obtained may be cracked due to too rapid gelling with respect to the formation of carbon dioxide. It is therefore necessary to adjust the rate of modification of toluylene diisocyanate according to the future application of the foam. In this regard, it can be noted that it is within the reach of the skilled person to make this adjustment by controlling, for example, directly and in a conventional manner, the viscosity of the product. Thus, in the case of catalyzed reactions, the degree of transformation can be controlled by introducing in particular into the reaction medium an agent deactivating the catalyst.

Thus, according to a particular embodiment, the mixture according to the invention comprises a chemically modified toluylene diisocyanate whose content of linkages - N = C = O is between 60 and 94% relative to that of the starting toluylene diisocyanate (i.e. a content from 6 to 40% lower than that of the starting toluylene diisocyanate). Preferably, the content of -N = C = O bonds is between 80 and 90% relative to that of the starting toluylene diisocyanate (ie a content of 10 to 20% lower than that of the starting toluylene diisocyanate) and more in particular, this is between 83 and 85% relative to that of the starting toluylene diisocyanate (ie a content of 15 to 17% lower than that of the starting toluylene diisocyanate).

The mixture according to the invention also comprises 1,6-hexamethylene diisocyanate. This can be used either in the form of purified monomer, or in the form of crude product. By crude 1,6-hexamethylene diisocyanate is meant 1,6-hexamethylene diisocyanate mixed with its polymerization products; the latter having higher or lower degrees of polymerization. The term “polymerization products” means more precisely the dimer, trimer, biuret and imino-uretidinone of 1,6-hexamethylene diisocyanate.

According to a particular embodiment of the invention, the crude 1,6-hexamethylene diisocyanate has a content of polymerization products of between 17 and 88% by weight of crude 1,6-hexamethylene diisocyanate. Preferably said content is less than 50% by weight of 1,6-hexamethylene diisocyanate.

In the case where 1,6-hexamethylene diisocyanate is used in the form of a purified monomer, this more particularly has a purity greater than 99.5%. According to a preferred embodiment of the invention, the purity of the monomer is greater than 99.8%.

The monomeric 1,6-hexamethylene diisocyanate has the advantage of greater simplicity of implementation. Indeed, it is not necessary to filter the monomer, prior to its use, since it does not contain insoluble compounds, whereas this may be the case during an implementation of the invention with a mixture comprising crude 1,6-hexamethylene diisocyanate. In addition, the low acidity of the monomeric 1,6-hexamethylene diisocyanate does not generally modify the acidity of the mixture and therefore does not change the foaming kinetics.

As stated above, the mixture according to the invention comprises chemically modified toluylene diisocyanate and 1,6-hexamethylene diisocyanate; the latter compound being present in an amount between 0.5 and 30% by weight of said mixture of isocyanates.

Preferably, the amount of 1,6-hexamethylene diisocyanate varies between 1 and 20% by weight of the above-mentioned mixture. More particularly, this varies between 2.5 and 10% by weight of said mixture.

Advantageously, the two aforementioned products are brought into contact by simple mixing, in the presence or absence of a solvent.

The use of the mixture according to the invention will now be described.

Obtaining high elasticity polyurethane foams from the above-mentioned mixture is carried out by carrying out a polyaddition reaction of the isocyanates with at least one compound of the polyether-polyol type.

As has been said before, the use of physical blowing agent to effect the reaction is not mandatory. In the case where such an agent is however used, the latter is chosen from agents known to those skilled in the art, and more particularly among agents that are not affected by the Montreal Protocol, such as chlorofluorocarbons, for example.

But according to a preferred embodiment of the invention, the reaction is carried out in the presence of a chemical blowing agent and more particularly in the presence of water.

The polyaddition reaction can be carried out with any type of polyether polyol known to a person skilled in the art. According to a particular embodiment of the invention, the polyether polyols used have a number average molecular weight of between 4800 and 6500.

Of course, additional additives can be used, such as in particular catalysts, such as tertiary amines, surfactants such as silicones or other silylated compounds, cross-linking agents such as glycerin.

The following examples illustrate the invention without limiting its scope.

EXAMPLES

• TDI représente le 2,4-toluylène diisocyanate.
• HDI représente le 1,6-hexaméthylène diisocyanate.
• NCO représente la liaison isocyanate -N=C=O et OH la liaison hydroxyl - OH.
• p représente des parties en poids
• L'index I correspond à la formule suivante : $$\text{I =}\frac{\text{nombre de groupements de NCO introduits}\hfill }{\text{nombre de groupements OH introduits}\hfill }\text{x 100}$$
  
• Le protocole de mesure de la déformation conformément à la norme NF-T56-112 est le suivant :

In what follows:

• TDI represents 2,4-toluylene diisocyanate.
• HDI represents 1,6-hexamethylene diisocyanate.
• NCO represents the isocyanate bond -N = C = O and OH the hydroxyl bond - OH.
• p represents parts by weight
• Index I corresponds to the following formula: $$\text{I =}\frac{\text{number of NCO groups introduced}\hfill }{\text{number of OH groups introduced}\hfill }\text{x 100}$$
  
• The deformation measurement protocol in accordance with standard NF-T56-112 is as follows:

The test pieces are in the form of parallelepipeds 50 mm high, with a square base 100 mm side.

The initial height (Do) is measured at a pressure of 0.1 kPa (load of 1 Newton) using a dynamometer working in compression.

- taux de compression :

70 %

- atmosphère de référence :

EH 95 % humidité relative

- température :

50°C

- durée :

22 heures

The samples are compressed in an oven under the following conditions:

- compression ratio :

70%

- reference atmosphere:

EH 95% relative humidity

- temperature :

50 ° C

- duration:

22 hours

On leaving the oven, the test piece is released from the test device.

The test pieces are left to stand at 23 ° C, 50% EH for 30 minutes.

The residual thickness (Df) of the test pieces is measured under the preload conditions described above.

The remanent deformation (D) after compression at constant deformation, expressed as a percentage, is given by the following formula in which (Dc) is the thickness under compression: $$\text{D =}\frac{\text{Do-df}}{\text{Do-dc}}\text{x 100}$$

Examples 1 to 5 :

A polyol mixture is produced having the following composition: - ARCOL POLYOL 1372 ™ (ARCO company) 100 p - Water 3.1 p - Glycerin 0.8 p - Surfactant: TEGOSTAB B4113® (company GOLDSCHMIDT) 0.5 p - 1,4 - Diazabicyclo (2,2,2) octane in 33% solution (company Air Product) 0.5 p - Dimethylaminopropylamine 0.4 p - ARCOL POLYOL 1180 ™ (ARCO company) 0.6 p - Trichloroethyl phosphate 2 p

The following polisocyanate mixtures are produced: Polyisocyanate mixtures Biuretized TDI nb.NCO / 100g = 0.96 HDI monomer nb.NCO / 100g = 1.19 nb.NCO in 100g of the mixture Ex 1 97.5% 2.5% 0.966 Ex 2 95% 5% 0.971 Ex 3 92.5% 7.5% 0.977 Ex 4 90% 10% 0.983 Ex 5 comp. 100% 0% 0.960

The percentages in this table are expressed by weight relative to the total amount of TDI and HDI present in said mixture.

Each of these mixtures is added to the polyol composition described above in such a way that the amount of the mixture added makes it possible to obtain foams whose index I is 104.2.

20 liters of foam are produced from the total mass of the reagents in a cylindrical expansometer thermostatically controlled at 23 ° C. at the base of which is a pressure sensor allowing the recording of the pressure during foaming (measurement of the duration of initiation, duration at peak and maximum pressure at peak).

After 72 hours of storage at atmospheric pressure at 23 ° C, in an atmosphere at 50% relative humidity (HE), the foam blocks are cut into parallelepipeds 50 mm high with a square base 100 mm side.

Table 1 summarizes the foaming characteristics, the density of the foams obtained, the results of the residual deformation measurements carried out on these foams, according to the protocol given above: Table 1 CHARACTERISTICS Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 comp. Duration initiation (s) 16 16.5 17 19 16 Duration at peak (s) 91 85 88 91 88 Pressure at peak (hPa) 6.4 8.2 6.5 7.1 7 Core density (kg / m ³ ) 34.6 36.9 35.9 38.4 34.5 D (%) 14 11 11 9 29

The same polyol composition is used at index I of 90 with the polyisocyanate mixtures described above.

The foaming characteristics and the properties of the foams are collated in the following table 2: Table 2 CHARACTERISTICS Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 comp. Duration initiation (s) 22 22 22 22 18 Duration at peak (s) 82 82 82 82 82 Pressure at peak (hPa) 6.9 7.9 6.9 8 8.8 Core density (kg / m ³ ) 38 39.2 40 41.2 36.6 D (%) 14 14 9 9 50

The comparison between Tables 1 and 2 shows that the residual deformation of the foams according to the invention is not affected by the modification of the index I, whereas it has doubled in the case of conventional foams.

Examples 6 to 10 :

The same polyisocyanate mixtures TDI and HDI monomer as those used in comparative examples 1 to 5 (respectively corresponding to comparative examples 6 to 10) are used at index I of 104.2 with a polyol composition identical to that of examples 1 to 5 comparative, but containing 4.3 parts of water.

The results obtained are collated in Table 3 below: Table 3 CHARACTERISTICS Ex 6 Ex 7 Ex 8 Ex 9 Ex 10 comp. Duration of initiation (s) 22 22 25 25 22 Duration at peak (s) 100 106 112 109 106 Pressure at peak (hPa) 7.2 8.6 10.3 9.3 8 Core density (kg / m ³ ) 27 27.8 27.1 29.3 25.7 D (%) 67 47 28 14 87

The table above shows that the foams prepared according to the invention have an improved residual deformation compared to conventional foams, even under very unfavorable conditions, that is to say with high water contents.

Examples 11 to 15

The same polyisocyanate mixtures TDI and HDI as those used in comparative examples 1 to 5 are used at index I of 90 with a polyol composition identical to that of comparative examples 1 to 5 but containing 4.3 parts of water .

The results obtained are collated in Table 4 below: Table 4 CHARACTERISTICS Ex 11 Ex 12 Ex 13 Ex 14 Ex 15 comp. Duration of initiation (s) 22 23 23 24 22 Duration at peak (s) 97 97 103 97 100 Pressure at peak (hPa) 7.8 6.9 7.5 9.2 9.6 Core density (kg / m ³ ) 28.6 30.6 29.1 32.9 27.1 D (%) 69 50 35 19 94

The lift of the foams obtained in Comparative Examples 13 and 15 was measured at various degrees of compression.

The results are collated in Table 5 below: Table 5 Examples Lift (hPa) according to compression (%) 25% 40% 50% 65% 13 10.5 13.3 17.3 31.6 15 comparison 13.1 16.6 21.4 38.9

This table indicates that the foams according to the invention have a lower lift than conventional foams.

Examples 16 to 20

Mixtures of biuretized TDI are carried out with crude HDI (containing 53% of free HDI and 47% of heavy HDI): Polyisocyanate blend Biuretized TDI nb.NCO / 100g = 0.944 HDI gross nb.NCO / 100g = 0.956 nb.NCO / 100 g of the mixture Ex 16 97.5% 2.5% 0.944 Ex 17 95% 5% 0.944 Ex 18 92.5% 7.5% 0.945 Ex 19 90% 10% 0.945 Comparative Ex 20 100% 0% 0.944

These isocyanate mixtures are used with the polyol mixture used in Comparative Examples 6 to 10 (containing 4.3 p of water) at index I of 104.3.

The results obtained are collated in Table 6 below: Table 6 CHARACTERISTICS Ex 16 Ex 17 Ex 18 Ex 19 Ex 20 comp. Duration of initiation (s) 19 25 24 25 19 Duration at peak (s) 91 97 94 103 91 Pressure at peak (hPa) 6.3 5.8 5.9 5.1 8.6 Core density (kg / m ³ ) 29.2 29.9 30.4 30.4 27.2 D (%) 41 19 14 11 76

These polyisocyanate mixtures are used with the polyol blend used in Examples 6 to 15 (comparative (containing 4.3 p of water)) at index I of 90.

The results obtained are collated in Table 7 below: Table 7 CHARACTERISTICS Ex 16 Ex 17 Ex 18 Ex 19 Ex 20 comp. Duration of initiation (s) 22 22 22 22 22 Duration at peak (s) 88 88 91 97 85 Pressure at peak (hPa) 7.1 6.8 5.8 4 11 Core density (kg / m ³ ) 29.8 30.8 31.9 32.9 28.9 D (%) 39 17 11 8 78

Claims (11)

1. A mixture of polyisocyanates, characterized in that it comprises chemically modified tolylene diisocyanate and 1,6-hexamethylene diisocyanate, the quantity of the latter being in the range 0.5% to 30% by weight of the mixture of isocyanates.
2. A mixture according to claim 1, characterized in that the quantity of 1,6-hexamethylene diisocyanate is in the range 1% to 20%, preferably in the range 2.5% to 10% by weight of the mixture of isocyanates.
3. A mixture according to claim 1 or claim 2, characterized in that the chemically modified tolylene diisocyanate is a tolylene diisocyanate derivative containing allophanate, biuret, urethane, urea, carbodiimide or isocyanurate type bonds.
4. A mixture according to the preceding claim, characterized in that the chemically modified tolylene diisocyanate is tolylene diisocyanate containing biuret type bonds.
5. A mixture according to any one of the preceding claims, characterized in that the chemically modified tolylene diisocyanate has a N=C=O bond content which is in the range 60% to 94% with respect to that of unmodified tolylene diisocyanate, more particularly said content is in the range 80% to 90%, preferably in the range 83% to 85%.
6. A mixture according to any one of the preceding claims, characterized in that the 1,6-hexamethylene diisocyanate is either in a purified or in an unrefined form.
7. A mixture according to claim 6, characterized in that the purified 1,6-hexamethylene diisocyanate is more than 99.5% pure, preferably more than 99.8% pure.
8. A mixture according to claim 6, characterized in that the unrefined 1,6-hexamethylene diisocyanate has a polymerisation products content which is in the range 17% to 88% by weight of unrefined 1,6-hexamethylene diisocyanate and preferably, said content is below 50% by weight of 1,6-hexamethylene diisocyanate.
9. The use of a mixture according to any one of claims 1 to 8 for the preparation of high elasticity flexible polyurethane foams, characterized in that the polyaddition process is carried out in the presence of at least one polyether-polyol.
10. Use according to claim 9, characterized in that said polyether-polyol has a number average molecular mass which is in the range 4800 to 6500.
11. Use according to claim 9 or claim 10, characterized in that the polyaddition process is carried out in the presence of a chemical blowing agent, preferably in the presence of water.